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Command Reference Guide
Global Configuration Mode Command Set
The VNS system in the AOS product implements preemptive and persistent caching of DNS records for
voice signaling protocols. The VNS system maintains a table of DNS records in a cache for voice signaling
protocols like SIP and MGCP. For example, if a request is generated from a SIP client (such as a SIP trunk
or SIP proxy), for which there is a configured SIP server entity (such as a proxy address or SIP server
address), the request is always serviced from the local DNS cache (rather than from an external DNS
server). This ensures that SIP access to DNS is always available immediately, even during transient DNS
outages.
The VNS system in AOS can be configured manually by adding a host to the cache (using the command
voip name-service host on page
1456) and by specifying the number of attempts used by VNS to verify the
DNS cache changes (using the command
voip name-service verification attempts <number> interval
<seconds> on page
1458). You can view the VNS cache by using the commands
show voip name-service
cache on page 825
and
show voip name-service name-table on page
826.
Configuring an FQDN using the voip name-service host command forces the FQDN resolution (using
DNS) to never timeout from the DNS name table. Each DNS record has a time to live (TTL) value that
specifies the amount of time to cache the record. After this time, the DNS table (by default) removes the
record from the cache. VNS issues DNS queries in an attempt to keep voice-related records cached in the
DNS name table, but if the DNS name servers are not available, the records can expire from the DNS
name table. The records associated with configured VNS host FQDNs are not flushed from the cache
regardless of the TTL or age of the record, but rather are permanently cached dynamic resolutions.
Command History
Release A4.03
Command was introduced.
Usage Examples
The following example adds the SIP host example.user.net to the VNS/DNS cache, using TCP requests:
(config)#voip name-service host example.user.net sip tcp
60000CRG0-35E
Copyright © 2012 ADTRAN, Inc.
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